This application is based on, and claims priority to Japanese Patent Application 9-208137, filed Aug. 1, 1997 in Japan, and which is incorporated herein by reference.
The present invention relates in general to an optical scanner, and in particular, to a method of and device for reducing the beam diameter of separate light beam components emitted from a common light source for optical scanner.
Point of Sale (POS) systems, such as optical scanners, capable of detecting and reading light reflected from a bar code attached to a commodity are widely used. For example, optical scanners, which are also referred to as bar code readers, are used at xe2x80x9ccheck-outxe2x80x9d counters in grocery stores to scan a bar code attached to a commodity such as a food product. By manipulating the commodity, these optical scanner systems provide an operator, such as a cashier, using the system to reduce the amount of time it takes to xe2x80x9cscanxe2x80x9d information about the commodity, reducing the burden on the operator and increasing the operator""s efficiency.
In recent years, optical scanners with two reading windows have been developed. The two windows are provided, for example, in the bottom and front portions of the optical scanner, forming an xe2x80x9cLxe2x80x9d shape. The two windows enable the optical scanner to read and scan from multiple directions bar codes attached to commodities. Hence, a bar code attached to a commodity may be detected and read from light sources emitting from both windows, despite differing orientations of the bar code on the commodity. This feature further lightens the burden imposed on the operator. However, conventional optical scanners with multiple windows require separate optical scanners for each window. The result is a costly, complex optical scanner with numerous parts and which is large in size.
For example, optical scanners which have reading windows respectively provided in both the bottom and front portions thereof require optical scanning systems for each of the reading windows. Each of the optical scanning systems includes a light source, scanning means such as a polygon mirror, and other mirrors. Thus, the scanner is complex and requires a large number of components or parts, which increases the manufacturing costs. However, if a common light source is used for both of the optical scanning systems, the required number of parts and the costs associated therewith decrease.
The use of a common light source 1 in an optical scanner 100 is shown in FIG. 27. FIG. 27 is an exemplary prior art diagram illustrating a conventional optical scanner 100 with a common light source 1 and used, for example, to scan a bar code attached to an object. To use a common light source 1 in the optical scanner 100 shown in FIG. 27, a light splitting device 2, such as a half mirror (semi-transparent mirror), is used to split a common light source 1 into a first light beam component X and a second light beam component Y. The first and second light beam components X and Y, respectively, are then directed to a common polygon mirror 3, either directly or through another mirror. Light beam component X is then emitted through a group of mirrors M1 from reading window 4 (provided in the bottom portion of the optical scanner 100), and light beam component Y is emitted through a group of mirrors M2 from reading window 5 (provided in the front portion of the optical scanner 100). The emitted light beam components X and Y then impinge on, for example, a bar code attached to an object passing through the emitted light, which reflects back to the optical scanner 100. The bar code is read by the optical scanner 100 by detecting the reflected light by detectors 6 and 7.
In order to more accurately read a bar code, and in particular, a bar code having narrow spaces between adjacent bars, the beam width of the light beam scanning the bar code must be sufficiently reduced. To reduce the beam width of the light beam scanning the bar code, for example, light beam components X and Y (shown in FIG. 27), a beam shaping device 8 is placed between the common light source 1 and the light splitting device 2. Moreover, it is also necessary not only to reduce the diameter of the light beam components X and Y, but to reduce the diameter at a desired position. That is, the diameter of the beam size must be sufficiently reduced at the desired position, particularly the position where the object is being scanned.
As the width of the bars in the bar code narrows, it becomes increasingly difficult for an emitted light source to read the bar code. A desirable solution to reading bar codes having narrow spaces between bars would be to use a common light source 1 having a smaller diameter. As discussed above, it is desirable to xe2x80x9csplitxe2x80x9d the common light source 1 (i.e., laser beam) into first and second laser beam components X and Y, such that the bar code may be read or scanned from multiple directions (from a bottom portion and a front portion of the optical scanning device). Using the first and second laser beam components X and Y, respectively, an xe2x80x9coptimum reading zonexe2x80x9d is established by defining first and second focal points of the first and second laser beam components X and Y, respectively. It is desirable that the focal point (a point at which the laser beam has the smallest diameter) of the laser beam is established near the reading center the optimum reading zone. In this regard, the common light source 1 is able to read and scan the bar code with increasing efficiency when the two focal points are directed towards the same location. To accomplish this, it is desirable that the distance from the light source from which the scanning light (light beam component X in FIG. 27) emitted from the bottom reading window 4 to the reading center is equal to the distance from the light source from which the scanning light (light beam component Y in FIG. 27) emitted from the side reading window 5 to the reading center.
However, due to the complexity of the optical components in the optical scanner for prior art, it is difficult to equalize these distances and may result in the focal point of the first light beam component X being set at the center of the optical reading zone, and the focal point of the second light beam component Y being set off-center of the optimal reading zone. In that case, the bar code cannot be read using the second scanning light. Hence, achieving optimal first and second focal points is hindered, resulting in the failure of one of the laser beam components from reading or scanning the bar code as it passes through the xe2x80x9coptimum reading zonexe2x80x9d.
Thus, there exits a need for a cost effective optical scanner having multiple windows which reduces the overall size of the scanner by reducing the number of components required therein. Additionally, there exists a need for an optical scanner having multiple windows capable of reading and scanning a bar code using a common light source.
An object of the present invention is to provide an optical scanner which reduces the beam diameters of two light beam components into which a light beam emitted from a common light source is split by an optical beam splitter.
Another object of the present invention is to provide an optical scanner which is provided with a common light source and two reading windows, and which can read a bar code with good sensitivity by using light beams respectively emitted from the reading windows.
In accordance with one embodiment of the present invention, an optical scanner includes a body, at least one reading window provided in the body, a light source, light splitting means for splitting a light beam emitted from the light source into a first light beam component traveling along a first optical path, and a second light beam component traveling along a second optical path. Also provided in the optical scanner of the present invention are light scan means allowing the first light beam component and the second light beam component to be emitted from the reading window, first beam shaping means placed between the light source and the light splitting means, and second beam shaping means placed in one of the first and second optical paths.
In accordance with another embodiment of the present invention, an optical scanner includes a body, a first reading window provided in the body, a second reading window provided in the body at an angle with the first reading window, a light source, and light splitting means splitting a light beam emitted from the light source into a first light beam component traveling along a first optical path and a second light beam component traveling along a second optical path. Also provided are scan means allowing the first light beam component and the second light beam component split by the light splitting means to be emitted from the first reading window and the second reading window, at least one detector detecting the light beam which is emitted from the reading windows and impinges on and is reflected by an object, first beam shaping means placed between the light source and the light splitting means, and second beam shaping means placed in one of the first and second optical paths.
In the above-mentioned embodiments of the present invention, a light beam emitted from the light source is shaped by the first beam shaping means in such a manner as to have a reduced beam diameter at a desired position. However, in some cases, each of the two light beam components split by the light splitting means does not have a minimum beam diameter at a desirable position. To solve this problem, the first beam shaping means reduces one of the two light beam components at a desired position, and the second beam shaping means is placed in the optical path of the other light beam component, correcting the position of the light beam to a desired position. Hence, each of the two light beam components split by the light splitting means has a minimum beam diameter at a desired position.
In accordance with another embodiment of the present invention, the scan means comprises a polygon mirror reflecting the first and second light beam components split by the light splitting means, at least one mirror placed between the light splitting means and the polygon mirror, a first group of mirrors causing the first light beam component reflected by the polygon mirror to be emitted from the first reading window, and a second group of mirrors causing the second light beam component reflected by the polygon mirror to be emitted from the second reading window.
In accordance with still another embodiment of the present invention, there is provided an apparatus for scanning an object having a bar code attached thereto. The apparatus comprises a body including first and second reading windows emitting and receiving a light beam, a light splitting device splitting the beam of light emitted from a light source into first and second beam components, a light scan device for directing the first beam component and second beam component through the respective first and second reading windows, a first beam shaping device, a second beam shaping device, and a first and second detector for detecting the first and second beam components, respectively.
In accordance with yet another embodiment of the present invention, there is provided a light source module. The light source module comprises a light source, first and second beam shaping means, a light splitter splitting a light beam which is emitted from the light source. The first beam shaping means shapes a cross-sectional shape of the light beam and the second beam shaping means changes a focal distance of the light beam.
In accordance with another embodiment of the present invention, there is provided a light source module. The light source module comprises a light source, a beam shaping device, a light splitter splitting a light beam which is emitted from the light source into first and second light beams. The beam shaping device changes a focal position of one of the first and second light beams to a position in from of or beyond a focal position of the other one of the first and second light beams.
In one aspect of the present invention, the first beam shaping means reduces the light beam diameter at a first distance from the light source, and the second beam shaping means reduces the beam diameter of the light beam traveling along an optical path at a second distance from the light source which is different from the first distance.
In another aspect of the present invention, the first beam shaping means includes a collimator lens and an aperture.
In still another aspect of the present invention, the second beam shaping means comprises a convex lens whose focal length is greater than the collimator lens. Alternatively, the second beam shaping means comprises a concave lens, or a concave mirror.
In a further aspect of the present invention, the light source, the light splitting means and the first beam shaping means are formed as one unit.
In yet another aspect of the present invention, the light source, the light splitting means, the first beam shaping means and the second beam shaping means are formed as one unit.
In accordance with another embodiment of the present invention, a method for scanning an object using an optical scanner splits a light beam emitted from a light source, emits first and second beams respectively through first and second reading windows, scans the first and second beam components through the first and second reading windows such that the emitted light cross paths at an optical reading position, shapes the light beam and first or second beam components to minimize the diameter of the both the first and second beam components at the optical reading position, and detects the object.
These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.